Multiplicity and transverse energy distributions associated to rare events in nucleus-nucleus collisions

We show that in high energy nucleus-nucleus collisions the transverse energy or multiplicity distribution PC, associated to the production of a rare, unabsorbed event C, is universally related to the standard or minimum bias distribution P by the equation PC(ν) = ν〈ν〉P(ν), with ΣP(ν) = 1 and ν ≡ ET or n. Deviations from this formula are discussed, in particular having in view the formation of the plasma of quarks and gluons. This possibility can be distinguished from absorption or interaction of comovers, looking at the curvature of the JΨ over Drell-Yan pairs as a function of ET.